LONDON (Reuters) - A leading specialist on al Qaeda said on Tuesday an Egyptian veteran militant was acting as an interim operational leader pending the expected appointment of deputy chief Ayman al-Zawahri as successor to Osama bin Laden.

Noman Benotman, a former associate of bin Laden and now an analyst with Britain's Quilliam Foundation think tank, told Reuters Saif al-Adel was operating in effect as interim leader while the organisation collected pledges of loyalty to Zawahri.

U.S. prosecutors say Adel is one of al Qaeda's leading military chiefs, and helped to plan the bomb attacks against the American embassies in Nairobi and Dar es Salaam in 1998 and set up training camps for the organisation in Sudan and Afghanistan in the 1990s.

There was no immediate independent confirmation of the report, which Benotman said was based on his own contacts in jihadist circles.

"This role that he has assumed is not as overall leader, but he is in charge in operational and military terms," he said.

"This has happened in response to the impatience displayed by jihadists online who have been extremely worried about the delay in announcing a successor."

"It is hoped that now they will calm down. It also paves the way for Zawahri to take over," he said, adding that Adel and Zawahri were close.

Benotman, who knew Adel personally when both were active as militants in Afghanistan, said Adel "already occupied a role akin to chief of staff" even before bin Laden's death in a U.S. raid in Pakistan on May 2.

Adel was believed to have fled to Iran after the U.S. invasion of Afghanistan after the Sept. 11 2001 attacks on the United States, and they were subsequently held under a form of house arrest there, according to some media reports.

Iranian authorities are reported by Arab media to have released him from custody about a year ago, and he then moved back to the Afghanistan-Pakistan border region.

Some analysts say that Adel, widely believed to have been in remote areas of northern Pakistan over the past year, has since returned to Iran, or to Afghanistan, in recent weeks.

Benotman, who is a former leader of the Libyan Islamic Fighting Group, which tried and failed to topple Libyan leader Muammar Gaddafi in the 1990s, said it was taking time to obtain pledges of loyalty to Zawahri from the far flung affiliates and branches of al Qaeda.

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